The present invention relates to a method and an apparatus for manufacturing, from a round rod-like metal wire, a hollow cylindrical tape guide for guiding magnetic recording tape, such as video tape or audio tape.
FIG. 1 shows cassette A containing a roll of magnetic recording tape (e.g., video tape or audio tape) and two tape guide rolls P for guiding the tape. Three methods of manufacturing tape guides P are known. In the first method, a thin blank punched out of a large thin metal plate is rolled into a hollow cylindrical roller. In the second method, a long metal pipe is cut into a short piece having a predetermined length, by means of sawing or grinding, and the short pipe is machined. The third method, which is disclosed in Japanese Patent Disclosure No. Sho 57-127951, comprises the following steps. First, as shown in FIG. 2, blank 1 (i.e., a round metal rod) is inserted into an opening of stationary die 2. Then, as is shown in FIG. 3, stepped punches 3 and 4 are pushed forward, one from each end of blank 1, until their stepped portion reach the ends of blank 1. In this way, a hollow cylindrical tape guide is formed which has thin wall 6 at the center and two holes. These holes are identical in shape and size to the end portions of punches 3 and 4.
The first method is difficult to perform. The second method is disadvantageous in two respects. First, when the metal pipe is sawed or ground, chips or dust will be formed, thus wasting the material. Secondly, a chamfering machine must be used to remove the burrs formed on the sawed surface.
The third method can indeed provide a tape guide having two holes having desired depth and diameter, but cannot always provide a tape guide having desired length and will thickness. More specifically, when blank 1 is too short, the tape guide will be to short, and wall 6 will be too thin. Conversely, when blank 1 is too long, the tape guide will be too long, and wall 6 will be too thick. In other words, the size of the tape guide changes in accordance with the length of blank 1. Further, the longer the blank, the greater pressure will be applied to die 2 as punches 3 and 4 are pushed into blank 1, one from each end of blank 1. In the worst case, die 2 may be broken. Moreover, due to wall 6 formed at the center of the tape guide, the entire tape guide cannot be mounted on a pin protruding from the bottom of cassette A. In order to mount the entire tape guide on the pin, wall 6 can be removed. When wall 6 is removed, however, burrs will be formed on the inner periphery of the tape guide. These burrs prevent the tape guide from smoothly mounting on the pin and, thus, from smoothly guiding the magnetic recording tape. Hence, the burrs must be removed.